Various devices have been designed for monitoring tidal volumes in animals and humans during sleep and anesthesia. These devices include the pneumotachograph, impedance pneumograph, mercury in rubber transducer, and body plethysmograph.
Yamada (U.S. Pat. No. 5,316,009) describes an apparatus with a pressure sensor for detecting pressure in an air passage connecting a lung ventilator and the airway system of a patient, and a flow rate sensor for detecting flow rate in the air passage. Shtalry (U.S. Pat. No. 5,271,412) describes a movement detector useful as an apnea monitor which includes a piezoelectric crystal transducer, a supporting member on one side of the transducer, and a collector member on the opposite side of the transducer. Kronberg (U.S. Pat. No. 5,273,036) describes a partial body plethysmograph to enable accurate modeling of a human's respiratory system for input frequencies of up to about 96 Hz using transfer impedance measurements. Jackson (U.S. Pat. No. 5,513,648) describes a method of measuring lung function in a subject including connecting a pneumotach in series with the subject's airway and taking pressure readings upstream and downstream of a fixed resistance element in the pneumotach.
The prior art devices present one or more disadvantages including inconvenience of use and costly production of the devices. Therefore, there is a need for a simple and reliable means for monitoring tidal volumes.
Gentile et al. (U.S. Pat. No. 5,086,785) describe a sensor for primarily detecting angular displacement of fingers of the hand, movement of arms and legs and joints. The angular displacement sensors may be disposed on a glove worn by a user such that the movements of the fingers of the user can be supplied as inputs to a computer to control robotics, video games, the movement of graphics, or other displayed materials on a display terminal. The sensor has a substrate and sensing means attached to the substrate and connectable to an electric circuit. Several embodiments are disclosed including a conductive elastomer sensor, a conductive ink sensor, a sliding resistor sensor, a force sensitive sensor, and a conductive fluid sensor.